Possible Causes

WARNING: This page is about a different car, the 2003 Mazda 6. However, it is still accessible from the selected car via links, so may be relevant.

Possible causes are:

Engine malfunction
Fuel filter clogged or restricted
Fuel leakage on fuel line from fuel distribution pipe and fuel pump
Fuel pump malfunction
Fuel return hose clogged
HO2S (RF, LF) deterioration
HO2S (RF, LF) heater malfunction
Insufficient compression
Leakage exhaust system
PCM malfunction
Pressure regulator malfunction
Purge solenoid hoses improper connection
Purge solenoid valve malfunction